We propose to study the relative genetic isolation with groups of strains of the same species as well as between species of the genus Staphylococcus, using the techniques of DNA-DNA hybridization. We also propose to study the relatedness of staphylococcal phages and the various plasmids found in staphylococci by similar techniques and by heteroduplex formation. The mechanisms of genetic exchange and the role of various barriers to exchange will be investigated.